Re: Terminate process that fails on a constrained allocation V3

[Andrew Morton <akpm@osdl.org>]

Christoph Lameter <clameter@engr.sgi.com> wrote:
>
> Some allocations are restricted to a limited set of nodes (due to memory
>  policies or cpuset constraints). If the page allocator is not able to find
>  enough memory then that does not mean that overall system memory is low.
> 
>  In particular going postal and more or less randomly shooting at processes
>  is not likely going to help the situation but may just lead to suicide (the
>  whole system coming down).
> 
>  It is better to signal to the process that no memory exists given the
>  constraints that the process (or the configuration of the process) has
>  placed on the allocation behavior. The process may be killed but then the
>  sysadmin or developer can investigate the situation. The solution is similar
>  to what we do when running out of hugepages.
> 
>  This patch adds a check before we kill processes. At that
>  point performance considerations do not matter much so we just scan the zonelist
>  and reconstruct a list of nodes. If the list of nodes does not contain all
>  online nodes then this is a constrained allocation and we should kill the
>  currnet process.

Looks sane, thanks.  I made constrained_alloc() inline, to give the
compiler the best-possible chance of eliminating the impossible-on-UMA
switch cases.